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[Arg 8 ]Vasotocin Excites Neurones in the Dorsal Vagal Complex in vitro : Evidence for an Action through Novel Class(es) of CNS Receptors
Author(s) -
Ingram C. D.,
Tolchard S.
Publication year - 1994
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1111/j.1365-2826.1994.tb00602.x
Subject(s) - vasotocin , medicine , endocrinology , vasopressin , receptor , agonist , oxytocin , neuropeptide , vasopressin receptor , biology , oxytocin receptor , receptor antagonist , chemistry , antagonist
Using extracellular recordings from brainstem slices in vitro , it was demonstrated that a high proportion (38/56) of neurones in the dorsal vagal complex of dioestrus, virgin female rats exhibit an excitatory response to [Arg 8 ]‐vasotocin (AVT). Pharmacological characterization suggests that these responses cannot be entirely explained by interaction with either of the currently known classes of central receptors for oxytocin (OT) and vasopressin (V 1a ). Comparison of the responses with those to the OT receptor‐specific agonist [Thr 4 ,Gly 7 ]‐OT (TGOT), showed that not all neurones that responded to TGOT also responded to AVT (3/27). Furthermore, while the effects of 10 −7 M TGOT could be blocked either by the broad‐spectrum antagonist d(CH 2 ) 5 [d‐Tyr(OEt) 2 ,Val 4 ,Cit 8 ]‐vasopressin or by the selective OT receptor antagonist d(CH 2 ) 5 [Tyr(Me) 2 ,Thr 4 ,Orn 8 ,Tyr‐NH 2 9 ]‐vasotocin, these peptides did not completely block the responses to AVT, indicating that AVT is unlikely to act through the central OT receptor. The responses to AVT and [Arg 8 ]‐vasopressin (AVP) indicated the presence of at least 2 classes of receptor with which these agonists could act. Of 42 neurones tested with both AVP and AVT, none responded to AVP in the absence of a response to AVT, while 7/42 responded to AVT without a response to AVP. This might be explained by AVP acting through only the V 1 receptor, while AVT acts through both the V 1 and its own novel class of receptor. This was substantiated by the fact that two OT/V 1 receptor antagonists, d(CH 2 ) 5 [d‐Tyr(OEt) 2 ,Val 4 ,Cit 8 ]‐VP and d(CH 2 ) 5 |Tyr(Me) 2 ,Tyr‐NH 2 9 ]‐AVP, were unable to block completely all the responses to AVT at a dose which suppressed responses to both AVP and TGOT. These data suggest that, in addition to activation by OT and AVP, neurones in the mammalian central nervous system are able to be excited by AVT, possibly involving its own distinct class of receptor.